Abstract: The reversed- phase chromatographic systems, either modified dynamically with ben-zyltrimethyl ammonium bromide or coated "permanently" with alkylpyridinium salts, have been studied for the separation and detection of hydroxy acids by the indirect photometric detecction. The ben- zyltrimethyl ammonium bromide and alkylpyridinium salts would play the part of a detection agent and a modifier in the indirect photometric chromatography. The adsorption isotherms of these reagents on YWG-CHreversed phase packing in methanol-aqueous phosphate buffer solutions are determined. The influence of the amounts of the reagents adsorbed on the stationary phase and that of other factors on the retention and detection sensitivity of hydroxy acids are illustrated.

Key words: Indirect photometric chromatography, Hydroxy acid, Alkylpyridinium salt